Grounded Neutral systems
Grounded Neutral systems
(OP)
well i am having some confusion as far as what the NEC requires for grounding your neutral on power distribution systems...
250.2 A (5) EFFECTIVE GROUND-FAULT CURRENT PATH-
Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the over-current device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. THE EARTH SHALL NOT BE CONSIDERED AS AN EFFECTIVE GROUND FAULT-PATH.
now the way i understand that is that Neutral should not be connected to ground because the only reason you do that is for ground fault-paths for overcurrent conditions or for disharmony within a transformer or genset. but there are also regs like 250.184B and C. can someone clarify this for me?
250.2 A (5) EFFECTIVE GROUND-FAULT CURRENT PATH-
Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the over-current device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. THE EARTH SHALL NOT BE CONSIDERED AS AN EFFECTIVE GROUND FAULT-PATH.
now the way i understand that is that Neutral should not be connected to ground because the only reason you do that is for ground fault-paths for overcurrent conditions or for disharmony within a transformer or genset. but there are also regs like 250.184B and C. can someone clarify this for me?






RE: Grounded Neutral systems
It appears that you haven't grasped the concept of system grounding and you need to take a few classes or sit down with a good electrical engineer friend.
Rafiq Bulsara
http://www.srengineersct.com
RE: Grounded Neutral systems
RE: Grounded Neutral systems
RE: Grounded Neutral systems
You may also want to look up IEEE Std. 1100. Recommended practice for grounding sensitive electronic equipment and systems.
Rafiq Bulsara
http://www.srengineersct.com
RE: Grounded Neutral systems
As well as providing a low impedance path to ground, grounding also establishes equi-potential zones. Your isolated neutrals often defeat the establishment of equipotential zones and create dangerous situations.
I have never heard of a comm, data or instrument problem caused by installing proper grounds. Most comm types are pretty narrowly focused and do not even realize that the power people have brought their equipment up to code.
If you go back about half a century, when POS data systems were coming into use, the data guys made a foolish assumption. They had problems. They then made further false assumptions as to the cause of the problems.
Not good engineering.
Had they chosen top check the electrical code, they would have found that the original installations were in violation of the codes. Had the original data installations been designed to be code compliant we would probably not have isolated neutrals today.
Try it the right way. You may be surprised to find that a code compliant installation DOES NOT cause the problems that an isolated ground is supposed to avoid.
By the way; The original issues were caused by comm types trying to save one data conductor.
Why am I wasting time trying to help a comm type with safe and effective grounding methods?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Grounded Neutral systems
RE: Grounded Neutral systems
Rafiq Bulsara
http://www.srengineersct.com
RE: Grounded Neutral systems
Your ground loops may not be an issue. Sometimes you get current sharing between a neutral and a ground. The problems that this can create in a large system with ground current protection may never arise on a small system.
Did you know that every properly wired, utility supplied home in North America has ground loops?
Tell us the voltages you have and need in the format that I suggested please.
Also, your transformer creates a serarately derived system. A ground connection at the generator and another at the transformer secondary will not create a ground loop.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Grounded Neutral systems
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Grounded Neutral systems
RE: Grounded Neutral systems
I hate to be blunt, but you and your employer need a power electrical engineer.
Rafiq Bulsara
http://www.srengineersct.com
RE: Grounded Neutral systems
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Grounded Neutral systems
First I am NOT advocating improperly grounded installations.
That said, I've seen many a smoked port where what was safe was not what would work, or otherwise made issues. [If "red side" "black side" and KG84 dredge up memories...]
For that reason, I have a mantra I often cite:
Fiber is your friend
Fiber just solves all end of messy comm problems. Ports worship the smoke god every time Mother Nature goes bowling? Crap floating on the data circuit return? Whatever... remember your friends. I can't even imagine how substation/gen plant SCADA systems ever worked in the pre-fiber era.
RE: Grounded Neutral systems
That said, I agree 100% about fiber solving all sorts of problems.
RE: Grounded Neutral systems
As you might guess from the responses, you have struck a nerve. I think you are well-intentioned, but there is a history of communications technicians creating fatalities over the past 50 years.
Alan
"The engineer's first problem in any design situation is to discover what the problem really is." Unk.
RE: Grounded Neutral systems
RE: Grounded Neutral systems
We could go on about all this, but I will spare the younger ones out there.
rasevskii
RE: Grounded Neutral systems
I started in pipelines; I recall tube-based Taylor PID process controls; it was a big step up from the pneumatic ones!
And we had a North Electric Paracode supervisory system, with relay array A-D converters; units, tens, hundreds, 0/1 thousand PSI. On bad nights, I can still hear them, and I'm not sure I have all the chart recorder ink off my fingers yet.
Is it any wonder I went back to get an EE degree?
RE: Grounded Neutral systems
RE: Grounded Neutral systems
Electronics techs are concerned with noise immunity under normal circumstances. In some cases, the optimum solution could lead to a hazardous condition during a fault. Or cause problems (loops) due to a lack of understanding of the function of various types of grounds (signal vs safety).